Search results for "Chain transfer"

showing 5 items of 85 documents

Über den Mechanismus der Entstehung von 1.3.5-Trioxacycloheptan bei der kationischen Polymerisation von 1.3-Dioxolan

1971

Die von MIKI, HIGASHIMURA und OKAMURA beschriebene Bildung von Trioxacycloheptan wahrend der kationischen Polymerisation von Dioxolan wird durch Spuren von Wasser verursacht und ist nicht auf die von MIKI et al. postulierte backbiting-Reaktion zuruckzufuhren. Wasser fuhrt durch Polymerisationsubertragung zu Hemiformal-Endgruppen, aus welchen Formaldehyd abgespalten wird, der dann zusammen mit Dioxolan Trioxacycloheptan ergibt. Die Trioxacycloheptankonzentration steigt schon nach kurzen Polymerisationszeiten nicht weiter an und ist direkt proportional der Menge an zugesetztem Wasser; dadurch ist eine bequeme und sehr empfindliche Bestimmung des Gesamtwassergehaltes im Polymerisationsansatz m…

chemistry.chemical_compoundPolymerizationChemistryDioxolanePolymer chemistryFormaldehydeCationic polymerizationChain transferDie Makromolekulare Chemie
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Darstellung von block- und pfropf-copolymeren des trioxane. 25. Mitt. Über polyoxymethylene

1965

Die kationische Polymerisation von Trioxan wird durch makromolekulare Verbindungen mit reaktionsfahigen COC-Gruppen wie Polyvinylacetat (PVA), Polyathylenterephthalat (PET), Poly-1,3-dioxolan oder Polyvinylbultyral (PVB) ubertragen. Dabei entstehen je nach der Art des makromolekularen Ubertragers Pfropf-Copolymere, Block-Copolymere oder vernetzte Copolymere. Die Produkte sind uberwiegend thermisch stabil. Bei der kationischen Polymerisation von Trioxan mus auch eine Ubertragung an den Acetalgruppen des Polyoxymethylens erwartet werden. Polymeric compounds with reactive COC groups such as polyvinyl acetate (PVA), polyethylene terephthalate (PET), poly-1,3-dioxolane or polyvinyl butyral (PVB)…

chemistry.chemical_compoundPolyvinyl butyralPolyvinyl acetateTrioxanechemistryPolyoxymethylenePolymerizationPolymer chemistryCationic polymerizationCopolymerChain transferDie Makromolekulare Chemie
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Concerning the reaction mechanism of the anionic polymerization of styrene in tetrahydrofuran

1969

chemistry.chemical_compoundReaction mechanismAnionic addition polymerizationchemistryGeneral EngineeringChain transferPhotochemistryIonic polymerizationTetrahydrofuranStyreneLiving anionic polymerizationJournal of Polymer Science Part B: Polymer Letters
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1984

A dimeric biradical •M plays a central role in the initiation of the spontancous polymerization of methyl methacrylate (M1). Besides the initiation step by chain transfer reaction, a change of the multiplicity of ˙M seems to be of importance. Evidence is given by heavy atoms in the solvent or in an inert gas atmosphere, leading to an acceleration of the overall polymerization rate. The observed effect is related to the atomic number of the respective heavy atom. Measurements of the temperature dependence of the effect for carbon tetrachloride show that — as expected — no activation energy is needed for this reaction step. The results are summarized in a reaction scheme for the initiation me…

chemistry.chemical_compoundReaction mechanismchemistryPolymerizationReaction stepRadical polymerizationPolymer chemistryLiving polymerizationChain transferSolution polymerizationMethyl methacrylatePhotochemistryDie Makromolekulare Chemie
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Effect of hydrogen on the ethylene polymerization process over Ziegler-Natta catalysts supported on MgCl2(THF)2. I. Studies of the chain-transfer rea…

2000

The effect of hydrogen on the molecular weight of polyethylene obtained over vanadium catalysts (based on VCl4 and VOCl3) supported on MgCl2(THF)2 was studied and the results were compared to those obtained for similar titanium catalysts. It was confirmed that the dependencies of the transfer reaction on the hydrogen concentration are a half-order in all investigated systems. However, the transition metal of the catalytic site affects the ratio of the transfer rate with hydrogen to the propagation rate (ktr,H/kp) and the results showed that hydrogen is a more effective agent of polyethylene molecular weight control in vanadium-based systems as compared to the titanium catalyst. © 2000 John …

inorganic chemicalsPolymers and PlasticsHydrogenInorganic chemistrychemistry.chemical_elementVanadiumChain transferGeneral ChemistryPolyethyleneSurfaces Coatings and FilmsCatalysischemistry.chemical_compoundTransition metalchemistryMaterials ChemistryZiegler–Natta catalystTitaniumJournal of Applied Polymer Science
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